On Tue, 23 Oct 2012 11:12:02 +0200, Daniel Vetter <daniel at ffwll.ch> wrote: > On Mon, Oct 22, 2012 at 12:55:55PM +0200, Daniel Vetter wrote: > > The overlay on the i830M has a peculiar failure mode: It works the > > first time around after boot-up, but consistenly hangs the second time > > it's used. > > > > Chris Wilson has dug out a nice errata: > > > > "1.5.12 Clock Gating Disable for Display Register > > Address Offset: 06200h???06203h > > > > "Bit 3 > > Ovrunit Clock Gating Disable. > > 0 = Clock gating controlled by unit enabling logic > > 1 = Disable clock gating function > > DevALM Errata ALM049: Overlay Clock Gating Must be Disabled: Overlay > > & L2 Cache clock gating must be disabled in order to prevent device > > hangs when turning off overlay.SW must turn off Ovrunit clock gating > > (6200h) and L2 Cache clock gating (C8h)." > > > > Now I've nowhere found that 0xc8 register and hence couldn't apply the > > l2 cache workaround. But I've remembered that part of the magic that > > the OVERLAY_ON/OFF commands are supposed to do is to rearrange cache > > allocations so that the overlay scaler has some scratch space. > > > > And while pondering how that could explain the hang the 2nd time we > > enable the overlay, I've remembered that the old ums overlay code did > > _not_ issue the OVERLAY_OFF cmd. > > > > And indeed, disabling the OFF cmd results in the overlay working > > flawlessly, so I guess we can workaround the lack of the above > > workaround by simply never disabling the overlay engine once it's > > enabled. > > > > v2: Add a comment in the code. > > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47827 > > Cc: stable at vger.kernel.org > > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> > > Tested-by: Rhys <rhyspuk at gmail.com> If you care to mention that you are not turning off the old w/a in case it has further side-effects, Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> -Chris -- Chris Wilson, Intel Open Source Technology Centre
